Short form of the question: How can I find technical specifications of
stock shock absorbers for common recent (1990+) sport motorcycles?
Motivation: Motorcycle entusiasts often desire to upgrade the
suspension of their motorcycles by replacing the shock absorber.
Custom shocks can be purchased from "racing" vendors starting at
around $400 and going up from there. Used stock shock absorbers from
other motorcyles can be found on eBay for less than $50. Obviously
this is the preferred choice for many people. This depends on knowing
what shocks are compatible and have the right characteristics.
These shock assemblies are a hydraulic damper surrounded by a coil spring.
Every shock absorber has a certain set of statistics about it, such as
stiffness, and damping characteristics. Some of those are adjustable,
which is a major bonus.
Knowing these specifications would allow a home mechanic to find a
shock absorber that fits and provides the desired handling
characteristic. For example, many owners of a Suzuki GS500 know that
a shock from a Suzuki Katana 600 is compatible, and provides a stiffer
suspension with adjustable rebound damping, both of which are
preferable. As far as I know, this information is obtained by trial
and error.
With specifications of widely available used shocks, a rider can
determine more mathematically what they want, and find the stock shock
that most closely matches that ideal. For example, if I look at the
stats of my current model (A GS500 in my case), which has a stiffness
of N kg/mm, I decide I want something 20% stiffer, or N*1.2 kg/mm.
Now I just find the shock that has close to that stiffness (ideally
all other variables the same), which might be something like a 1992
GSXR-750, and go shopping for a shock from that bike.
As far as I know, the major factors are:
length - the distance between the mounting holes (at rest)
width - the diameter of the spring coils
stroke - the distance the shock travels (the differece between the
fully extended and fully compressed lengths)
These three factors will determine if a piece even fits. If one of
these is wrong, then things are extremely bad. Other more qualitative
factors:
stiffness - technically the spring's constant, usually expressed in
kg/mm (even though kg is not a proper unit of force)
compression damping - how much it resists compression. (I don't know
the units or how this is measured)
rebound damping - resistance to extension.
There may be other factors. I am not an expert in this, and if there
is a resource which gives this information, it would be complete with
relevant data.
The aforementioned "racing" suspension dealers have some of this
information. They are not about to reveal it as it makes it possible
for people like me to not require their services. So the challenge is
to find the data from some other source.
Here is a web site describing some of the characteristics that are
interesting to motorcycle riders:
http://www.gostar-racing.com/information/motorcycle_suspension_set-up.htm |
